What is this artifact from baking?
This looks like the effect you get when you have 2 UVs in the exact same location.
If you're using the exact same UV on the other side, the bake gets info from both sides, giving these kinds of issues.
To fix this and still use the same UV, temporarily move 1 of the UVs of to the side of the UV-grid, bake your mesh, and move it back.